The hospital is four floors, plus the basement, and it's mostly buried. You can get in and out using a door on the roof, so you need to go all the way up. The pharmacy is north, so head for that. Using the left hand tunnel is fastest, and the entrance to the tunnels is just a house with two rooms left. It's a bottleneck, so a lot of people can end up stuck there together overnight trying to get in and out of the tunnels. If you can move fast enough, it might be safer to skip that house altogether and just keep moving into the residential area.